There exist numerous lower leg-immobilization devices, especially in alpine ski boots. These devices normally function either by means of the insertion of relatively thick removable shims between the upper and the lower leg, by changing the position of immobilizing elements permanently connected to the upper, or by modifying the length of one portion of the periphery of the upper, other than that part used for tightening adjustment.
These immobilizing devices prove indispensable, most often for proper adaptation to the morphology of the rear part of the lower leg, in particular in order to take into account variations of thickness of the calves and the position of the calves in relation to the height of the boot upper. These adjustment devices are also used to change the rearward support position of the lower leg in relation to the upper. When used in this way, the angled position of the median longitudinal axis of the lower leg changes in consequence in relation to the shell base of the boot, with respect to a given angled position of the longitudinal axis of this upper. In fact, the immobilizing devices thus used produce what is commonly termed adjustment of forward attitude.
As an example, mention may be made of Japanese Model of Utility No. 40-6561, which discloses a device incorporating a removable, reversible shim; of Swiss Patent No. 677 589 and French Patent No. 2,639,800, which describe devices in which the position of the adjustment elements can be changed, and French Patent Application No. 2 276 850, which relates to a shim designed to modify the length of one portion of the periphery of the upper, other than the tightening-adjustment portion.
These devices allow the lower leg to be secured in place; however, they pose a number of problems. In fact, in the examples of the removable shim and of the shim designed to modify a portion of the periphery of the upper, the shims in question must be detached in order to make the adjustment. This operation is difficult to perform outside of a sheltered area, since it requires that the top of the upper be released, or even that the boot be removed, and thus cannot be carried out correctly on ski runs, much less in snow. In addition, because the skims have to be dismantled, there is the additional risk of dropping them during the procedure, and, if not of losing them, of requiring a search and/or cleaning to ensure that they remain free of any dirt. In the case of devices whose immobilizing components can be changed while they are in position, the risk of loss of these components is not a factor; on the other hand, it is essential to have suitable tools for performing the operation properly, and also for releasing the top of the upper. It is obvious, moreover, that these devices have relatively complex structures, since they employ mobile metal parts that are movable translationally and reciprocally adjusted, for example using screw-nut assemblies. Such structures thus must be protected against infiltrations of snow, water, mud, etc., to prevent the soiling and/or deterioration of the metal parts composing them and to ensure that they remain easily maneuverable.